We converted Disneyworld hurricane passes to get in, and thereby ended up with (unexpected) 1 day parkhoppers. Hadnt planned CA at all, but figured that as it was included we might as well at least get fast passes from over there. We had time to do all the rides at DL (except nemo and dumbo), but in order to get some CA time we missed out on the shows (tiki room etc., and pirate island, steamboat and such). CA queues were practically non-existent even at midday though, so we managed to walk on to about 4 rides, fastpassed the river run, and also fit in muppets 3D and animation accademy.
That was a really full day, with less than an hour spent eating and no shopping time etc. So if you want to do ALL of DL and not starve, there is probably no point in hoppers, but if you are willing to sacrifice the tiki birds or similar then I think $20 would be well worth it for the amount of extra rides we got to do (plus CA and DL means that you can hold twice as many fast passes at once). I never really thought much of fastpasses till I had to get everything done in 1 day.